Voltage regulators and current regulators are well-known power regulators. Current regulators produce a regulated output having a predetermined current level, although the voltage level of the output may vary considerably while generating this controlled current level. Voltage regulators generate an output having a predetermined voltage level, although the current level of the output is permitted to fluctuate.
A variety of electronic devices employ both voltage and current regulators. For example, radio telephones include a voltage regulator to control the voltage supplied to electrical components, such as power amplifiers. For power amplifiers, the stability of the voltage supply is important as variations in the supply voltage level will vary the transmitted signal level, thereby introducing noise. It is therefor desirable to supply the power amplifier with a stable voltage level. Radio telephones may also include a current regulator to control the charging current applied to a rechargeable battery from an external source. The performance of the battery charger is dependent upon the charging current, so the charging current is carefully controlled during charging.
Electronic devices employing both current and voltage regulators use separate switching circuits for the current regulator and the voltage regulator. Although these separate regulators are effective to control their respective outputs to have a substantially constant output level, each switching circuit is relatively expensive and utilizes a substantial surface area of a printed circuit board (PCB) to which they are mounted. For small devices, the relatively large circuit board surface area required by the switching circuits can be a substantial hindrance to designers attempting to further reduce the size thereof.
Accordingly, it is desirable to provide voltage and current regulators in a smaller, less costly manner, while maintaining circuit performance.